Dehumidifiers of the kind set forth are commonly used to reduce dampness or condensation in a building.
The water that collects on the evaporator may freeze, but the dehumidifier periodically enters a defrost mode which allows the ice to melt. The water is collected in a water container, which usually includes a float switch that switches off the dehumidifier when the container is full. The defrost mode can be achieved in several ways:
1. A passive defrost system is sometimes used, in which the compressor is switched off for a fixed period every hour, i.e. there is a set running period and a set defrost period. The fan which draws air through the dehumidifier continues to run during the defrost period so that the incoming, relatively warm air eventually melts any buildup of ice on the evaporator.
2. In other cases a defrost heater may be included to melt ice on the evaporator. Again, the length of the defrost period is fixed, as is the length of the running period.
3. In hot gas bypass defrost systems, hot refrigerant from the compressor outlet is diverted by a solenoid valve directly into the frosted evaporator to melt the ice. In this case too, the defrost period is initiated for a preset period every hour (e.g. 5 minutes).